In some conventional systems, a transmitter may broadcast radio frequency (RF) signals. Generally, RF signals are generated by upconverting baseband signals to intermediate frequency (IF) signals, and then further upconverting the IF signals to RF signals, or directly upconverting from baseband signals to RF signals. The RF signals may be amplified by power amplifiers before being transmitted by a transmit antenna. Due to the proliferation of wireless devices such as telephones, walkie-talkies, personal digital assistants (PDAs), and routers in home computer networks, a transmitted signal may need to be at a certain minimum strength in order for a receiving device to demodulate the transmitted signal.
Generally, controlling output power of a transmitter is extremely important to minimize interference with other transmitted signals while still providing enough transmitted signal strength to be able to be received and processed by a receiver. In addition, a transmitter of limited power source, for example, mobile communication handset with a small battery, may need to accurately control power output in order to maximize battery life. However, a problem may be that performance of various electronic circuitry, for example, local oscillators (LO), may leak signals called LO feed-through (LOFT) to different parts of the transmitter (TX) signal path such that transmitted output consists of an LO tone. Unwanted DC components before an up-conversion mixer may also be up converted to RF output and result in an unwanted LOFT tone at the output of the transmitted signal. If left unabated, LOFT may result in undesired frequencies being transmitted, thereby corrupting the transmitted signal to make it unusable. Attempts to attenuate the LOFT may be referred to as LOFT cancellation.
Another problem may be in-phase and quadrature (IQ) imbalance, also called an image problem. The IQ imbalance comes from a mismatch between TX I path and TX Q path. The IQ imbalance may also corrupt the transmitted signal. Conventional transmitters may perform LOFT cancellation after performing gain control. After LOFT cancellation, IQ balance may not be maintained and IQ balance calibration may need to be done. Accordingly, the transmitter may need to perform both LOFT cancellation and IQ balance calibration when gain control is performed.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.